This invention relates to a current to voltage converter and in particular to a circuit which can convert an input current of either polarity to a fixed low voltage output of a single polarity.
In present integrated circuit technology, there are many areas where a low voltage source is needed. In particular, in telephone station sets, it is desirable to provide a variety of logic circuitry requiring a fixed voltage. For example, I.sup.2 L logic circuits operate on a voltage of 0.8 volts and above. Light emitting diode circuits are also finding increasing use for dial illumination and for providing a visual indication of hook status in multiple line service.
Such auxiliary circuitry is usually powered from local power at the customer's premises by means of a transformer. Although reliable, the transformer accounts for about one half of the on-premises installation cost. Further, accidental removal of the transformer from the local power outlet causes service problems.
It is therefore desirable to have such circuits operate from telephone line power. One problem which must be taken into account, however, is the frequent polarity reversals on the line. A further problem is to keep the AC impedance of the circuitry as low as possible so as not to adversely affect speech transmission. Although modifications can be made in the telephone circuit to compensate for loss of power, it would be more economical to retrofit auxiliary circuitry onto existing telephone sets.
It is therefore an objective of the invention to provide some means for converting telephone line power to a fixed voltage for retrofitting auxiliary circuitry onto present telephone sets while adding a minimum of AC impedance. It is a further objective of the invention to allow the circuit to operate from a single polarity regardless of any polarity reversals on the telephone line.